Hi everyone!
I´m working with a 6684A power supply (128 A max), but working with 30 A. The load is very low so is working in CC mode.
When I activate the OCP (overcurrent protection) it acts immediately and turn the output off, for example with 0,5V and 5 A that are
normal parameters for my load. I want to know if there is a way to limit the current, for example 40 A instead of the 128 A that the
power supply gives.

What you need to know is the difference between CV mode CC mode and OCP. With OCP off the power supply will automatically go between CV and CC mode depending on the Load that is put on it. If the load impedance goes low enough the power supply will transition from CV to CC and start regulating the output current. The OCP function when enabled turns off the output of the power supply when it transitions from CV to CC. The OCP function is not another mode but a function that monitors the mode the power supply is in and if it goes into CC shuts off the output. I have attached a graph showing the conditions for CV and CC operation.

Ok, thanks for your response. But, Is a way to limit the current the supply gives independently of the mode of work (CC or CV)? For example if the current is grater than 40 A that the output turns off, Could it be done?

The 6684A is capable of >5,000watts (40v/128amps), I'm not sure it would be my first choice for a 2.5watt (0.5v/5amp) application. However, if you are using the 6684A in the constant mode (at 5amps), I suggest to set the output voltage to 1.0volts and place a 0.025ohm/80watt resistor in series with the output.

This configuration will easily operate in constant current (5amps) up to 0.75volts across your load and still be current limited to 40 amps worst case.